As vehicles have developed over the years, the number of vehicular features and the ways in which those features may be adjusted (e.g., the number of feature modes) have increased dramatically. It is now common to provide a group of buttons or switches that a user (e.g., a driver) may utilize to adjust a vehicle's features to a preferential mode, and it is known to use resistor ladder networks in conjunction with these switches. Resistor ladder networks typically comprise a plurality of resistors and a plurality of switches disposed such that the closing of any one of the switches alters either the high resistance or the low resistance of a voltage divider circuit. The voltage divider circuit is comprised of a high resistance between a source of supply voltage and an output terminal and a low resistance between the output terminal and a low voltage reference, often referred to as ground. The resistor ladder is substituted for either the high resistance or low resistance in the voltage divider network. In this way, the resistance of the network is made variable and will exhibit a unique resistance range depending upon which switch is activated or depressed. Thus, the output voltage of the voltage divider is indicative of which, if any, of the switches are closed (i.e., user switch selection).
Certain vehicles have been designed that include clusters of control switches on and/or around the steering wheel of the vehicle for easy access by the driver. In fact, it has been found that a desirable switch assembly for this purpose includes nine such switches. Such switch assemblies may be configured to control, for example, an onboard telephone system or the vehicle's entertainment equipment. For example, with respect to the vehicle's radio, these switches may control power, volume, and tuning. In the case of a CD player, certain switches may be utilized for disk and/or track selection.
For automotive applications, an onboard processor must be able to distinguish between various voltages each corresponding to the activation of a specific switch or combination of switches. For this and other reasons, resistor ladder switch assemblies have been limited in the number of switches that they may employ. The problem is complicated due to supply voltage (e.g., battery) variations. That is, the battery voltage in a twelve volt automotive electrical system may, in fact, vary or drift between approximately nine volts and sixteen volts. Additionally, other operational conditions experienced in the vehicular environment may cause fluctuations in the battery voltage and the voltages appearing at the output of the ladder networks, including extreme temperature variations (e.g., −40 to 80 degrees Celsius), vibrations, and corrosive agents. Considering this, the output voltages associated with each switch state must be sufficiently separated from those associated with the other states to compensate for such fluctuations.
For the reasons described above, conventional switch assemblies having nine switches typically include a four-resistor ladder network and a five-resistor ladder network, although nine-position switch assemblies are known that are comprised of other combinations of ladder networks (e.g., a three-resistor ladder network and a six-resistor ladder network, three three-resistor ladder networks, etc.). In assemblies combining four- and five-resistor ladder networks, the output voltage of the four-resistor network is indicative of which, if any, of the four associated switches has been activated. Likewise, the output of the five-resistor network is indicative of which, if any, of the five associated switches has been activated. The output of the two ladder networks are provided to first and second input terminals of an onboard processor that monitors the two voltages and determines which, if any, of the nine switches have been activated by the driver. The need to utilize separate four-resistor and five-resistor ladder networks providing first and second output voltages, respectively, results in a more complex, costly, and cumbersome system.
Considering the above, it should be appreciated that it would be desirable to provide a resistor ladder switch assembly for use on a vehicle that includes a nine-position resistor ladder network having a single output voltage for discriminating amongst the nine switches. Furthermore, other desirable features and functions of the present invention will become apparent from the subsequent detailed description of the invention and the appended claims, taken in conjunction with the accompanying drawings and this background of the invention.